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/*
 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package java.time.temporal;

import java.time.Duration;

/**
 * A standard set of date periods units.
 * <p>
 * This set of units provide unit-based access to manipulate a date, time or date-time.
 * The standard set of units can be extended by implementing {@link TemporalUnit}.
 * <p>
 * These units are intended to be applicable in multiple calendar systems.
 * For example, most non-ISO calendar systems define units of years, months and days,
 * just with slightly different rules.
 * The documentation of each unit explains how it operates.
 *
 * @implSpec This is a final, immutable and thread-safe enum.
 * @since 1.8
 */
public enum ChronoUnit implements TemporalUnit {

  /**
   * Unit that represents the concept of a nanosecond, the smallest supported unit of time.
   * For the ISO calendar system, it is equal to the 1,000,000,000th part of the second unit.
   */
  NANOS("Nanos", Duration.ofNanos(1)),
  /**
   * Unit that represents the concept of a microsecond.
   * For the ISO calendar system, it is equal to the 1,000,000th part of the second unit.
   */
  MICROS("Micros", Duration.ofNanos(1000)),
  /**
   * Unit that represents the concept of a millisecond.
   * For the ISO calendar system, it is equal to the 1000th part of the second unit.
   */
  MILLIS("Millis", Duration.ofNanos(1000_000)),
  /**
   * Unit that represents the concept of a second.
   * For the ISO calendar system, it is equal to the second in the SI system
   * of units, except around a leap-second.
   */
  SECONDS("Seconds", Duration.ofSeconds(1)),
  /**
   * Unit that represents the concept of a minute.
   * For the ISO calendar system, it is equal to 60 seconds.
   */
  MINUTES("Minutes", Duration.ofSeconds(60)),
  /**
   * Unit that represents the concept of an hour.
   * For the ISO calendar system, it is equal to 60 minutes.
   */
  HOURS("Hours", Duration.ofSeconds(3600)),
  /**
   * Unit that represents the concept of half a day, as used in AM/PM.
   * For the ISO calendar system, it is equal to 12 hours.
   */
  HALF_DAYS("HalfDays", Duration.ofSeconds(43200)),
  /**
   * Unit that represents the concept of a day.
   * For the ISO calendar system, it is the standard day from midnight to midnight.
   * The estimated duration of a day is {@code 24 Hours}.
   * <p>
   * When used with other calendar systems it must correspond to the day defined by
   * the rising and setting of the Sun on Earth. It is not required that days begin
   * at midnight - when converting between calendar systems, the date should be
   * equivalent at midday.
   */
  DAYS("Days", Duration.ofSeconds(86400)),
  /**
   * Unit that represents the concept of a week.
   * For the ISO calendar system, it is equal to 7 days.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days.
   */
  WEEKS("Weeks", Duration.ofSeconds(7 * 86400L)),
  /**
   * Unit that represents the concept of a month.
   * For the ISO calendar system, the length of the month varies by month-of-year.
   * The estimated duration of a month is one twelfth of {@code 365.2425 Days}.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days.
   */
  MONTHS("Months", Duration.ofSeconds(31556952L / 12)),
  /**
   * Unit that represents the concept of a year.
   * For the ISO calendar system, it is equal to 12 months.
   * The estimated duration of a year is {@code 365.2425 Days}.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days
   * or months roughly equal to a year defined by the passage of the Earth around the Sun.
   */
  YEARS("Years", Duration.ofSeconds(31556952L)),
  /**
   * Unit that represents the concept of a decade.
   * For the ISO calendar system, it is equal to 10 years.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days
   * and is normally an integral number of years.
   */
  DECADES("Decades", Duration.ofSeconds(31556952L * 10L)),
  /**
   * Unit that represents the concept of a century.
   * For the ISO calendar system, it is equal to 100 years.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days
   * and is normally an integral number of years.
   */
  CENTURIES("Centuries", Duration.ofSeconds(31556952L * 100L)),
  /**
   * Unit that represents the concept of a millennium.
   * For the ISO calendar system, it is equal to 1000 years.
   * <p>
   * When used with other calendar systems it must correspond to an integral number of days
   * and is normally an integral number of years.
   */
  MILLENNIA("Millennia", Duration.ofSeconds(31556952L * 1000L)),
  /**
   * Unit that represents the concept of an era.
   * The ISO calendar system doesn't have eras thus it is impossible to add
   * an era to a date or date-time.
   * The estimated duration of the era is artificially defined as {@code 1,000,000,000 Years}.
   * <p>
   * When used with other calendar systems there are no restrictions on the unit.
   */
  ERAS("Eras", Duration.ofSeconds(31556952L * 1000_000_000L)),
  /**
   * Artificial unit that represents the concept of forever.
   * This is primarily used with {@link TemporalField} to represent unbounded fields
   * such as the year or era.
   * The estimated duration of the era is artificially defined as the largest duration
   * supported by {@code Duration}.
   */
  FOREVER("Forever", Duration.ofSeconds(Long.MAX_VALUE, 999_999_999));

  private final String name;
  private final Duration duration;

  private ChronoUnit(String name, Duration estimatedDuration) {
    this.name = name;
    this.duration = estimatedDuration;
  }

  //-----------------------------------------------------------------------

  /**
   * Gets the estimated duration of this unit in the ISO calendar system.
   * <p>
   * All of the units in this class have an estimated duration.
   * Days vary due to daylight saving time, while months have different lengths.
   *
   * @return the estimated duration of this unit, not null
   */
  @Override
  public Duration getDuration() {
    return duration;
  }

  /**
   * Checks if the duration of the unit is an estimate.
   * <p>
   * All time units in this class are considered to be accurate, while all date
   * units in this class are considered to be estimated.
   * <p>
   * This definition ignores leap seconds, but considers that Days vary due to
   * daylight saving time and months have different lengths.
   *
   * @return true if the duration is estimated, false if accurate
   */
  @Override
  public boolean isDurationEstimated() {
    return this.compareTo(DAYS) >= 0;
  }

  //-----------------------------------------------------------------------

  /**
   * Checks if this unit is a date unit.
   * <p>
   * All units from days to eras inclusive are date-based.
   * Time-based units and {@code FOREVER} return false.
   *
   * @return true if a date unit, false if a time unit
   */
  @Override
  public boolean isDateBased() {
    return this.compareTo(DAYS) >= 0 && this != FOREVER;
  }

  /**
   * Checks if this unit is a time unit.
   * <p>
   * All units from nanos to half-days inclusive are time-based.
   * Date-based units and {@code FOREVER} return false.
   *
   * @return true if a time unit, false if a date unit
   */
  @Override
  public boolean isTimeBased() {
    return this.compareTo(DAYS) < 0;
  }

  //-----------------------------------------------------------------------
  @Override
  public boolean isSupportedBy(Temporal temporal) {
    return temporal.isSupported(this);
  }

  @SuppressWarnings("unchecked")
  @Override
  public <R extends Temporal> R addTo(R temporal, long amount) {
    return (R) temporal.plus(amount, this);
  }

  //-----------------------------------------------------------------------
  @Override
  public long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive) {
    return temporal1Inclusive.until(temporal2Exclusive, this);
  }

  //-----------------------------------------------------------------------
  @Override
  public String toString() {
    return name;
  }

}
